There are two viruses of lower eukaryotes which code for highly specific killer toxins secreted by their respective hosts. One is the Saccharomyces cereviseae virus (ScV) and the other is the Ustilago maydis virus (UmV). S. cereviseae is important to the fermentation industry and U. maydis is an allergen which is significant in the midwest during late and early fall. The molecular biology of ScV is more thoroughly documented. Both are dsRNA viruses with separately encapsidated dsRNA genomes. In both viruses, large dsRNA segments of 3-4 md code for the capsid protein. In ScV medium sized segments of dsRNA (about 1 X md) code for toxin and in UmV there is presumptive evidence based on genetical analysis that dsRNA segments of about the same size code for the UmV toxin. In these studies biochemist W. H. Flurkey and I will purify and study the properties of the killer toxin produced by UmV infected U. maydis cells, produce antiserum against the toxin and use the toxin antiserum to distinguish which of the UmV dsRNA segments codes for it. In further studies we will use in vitro and in vivo experiments to define the processing steps which lead from the initial translation product to the native toxin. This research will test the hypothesis that there is a common mechanism for toxin secretion in these virus-infected lower eukaryotes.